Manufacture of flexible corrugated seamless metal tubing



E. T. CANDEE June 12, 1956 MANUFACTURE OF FLEXIBLE CORRUGATED SEAMLESSMETAL TUBING 3 Sheets-Sheet 1 Original Filed April 12, 1946 EQJE 51.40

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ATTORNE Y5 June 12, 1956 E. T. CANDEE 2,749,963

MANUFACTURE OF FLEXIBLE CORRUGATED SEAMLESS METAL TUBING Original FiledApril 12, 1946 3 Sheets-Sheet 2 INVENTOR. 17/3200? 7. Carla?! ATTORNEYSJune 12, 1956 E. T. CANDEE r 2,749,963

MANUFACTURE OF FLEXIBLE CORRUGATED SEAMLESS METAL TUBING Original FiledApril 12, 1946 3 Sheets-Sheet 3 TIE-l7 1 15.15 7 71 7d 72 III INVENTORBY m 50%.; M u.

ATTORNEYS United States Patent MANUFACTURE OF FLEXIBLE CORRUGATEDSEAMLESS METAL TUBING Ellsworth T. Candee, Watertown, Conn., assignor toTechnicraft Laboratories, Inc., a corporation of Connecticut vided andthis application November 16, 1950, Serial No. 196,049

12 Claims. (Cl. 153-73) This invention relates to the manufacture offlexible corrugated seamless metal tubing. The invention provides a newand improved method, and new and improved apparatus, for making suchtubing in rectangular or other polygonal cross-sectional shape. Thisapplication is a division of my copending application Serial No.661,903, filed April 12, 1946, now Patent No. 2,563,578, granted August7, 1951, in which I have described and claimed rectangular or otherpolygonal flexible corrugated seamless metal tubing as a new article ofcommerce, and in which I have described and claimed a flexible waveguide in which such tubing forms the fundamental flexible element.

Flexible corrugated seamless metal tubing of circular cross section,both with annular corrugations and with helical corrugations, has beenavailable for many years. Heretofore, however, it has not been possibleto produce polygonal tubing of this character. For those uses requiringflexible metal tubing of rectangular or other polygonal cross section,it has been necessary to employ tubing of the strip wound, mechanicallyinterlocked type, or other type of flexible metal tubing formed withseams.

The rectangular or other polygonal flexible corrugated seamless metaltubing provided by this invention is characterized by having a pluralityof deep narrow corrugations spaced apart a distance approximating theirdepth. (In referring to the corrugations as being spaced apart adistance approximating their depth, both throughout the specificationand in the claims, I mean that the ratio of spacing to depth of thecorrugations is small enough to render the tubing quite flexible, but donot mean that it is necessarily 1:1 it may vary, for example, from 1:3to 3:1, or over an even somewhat wider range, depending upon suchfactors as size of the tubing, actual depth of the corrugations, wallthickness, etc.) The outer surface of the corrugations at the corners ofthe tubing is generally formed with a substantial radius of curvature ina plane normal to the axis of the tubing. These corrugations render thetubing extremely flexible, and permit it to be bent readily through ashort radius.

Seamless corrugated flexible metal tubing of polygonal cross section ismade in accordance with the invention by forming an outward peripheralbulge on a seamless polygonal metal tube, and subsequently squeezing thebulge at its base to narrow and deepen it into a corrugation. Theinitial bulging of the tube advantageously is effected under conditionssuch that somewhat greater bulging pressure is applied at the corners ofthe tube than at the sides, thus assuring adequate bulging of the tubewall at the corners to form, in the subsequent squeezing operation,full-depth, unwrinkled and unruptured corrugations even at these pointsof maximum metal deformation. The initial outward peripheral bulging ofthe tube may be effected by applying pressure to a deformable pluglocated within the tube, while the tube is positioned within an openingin a die plate configured to limit bulging of the metal and to preventimproper deforming of the tube.

2,749,963 Patented June 12, 1956 The apparatus provided by the inventionfor making seamless corrugated flexible metal tubing of rectangular orother polygonal cross section comprises a pair of separable die platesdefining between them a polygonal die opening. At least one peripheralgroove is formed in the die plate walls of said opening. Meansadvantageo'usly in the form of a deformable but substantiallyincompressible plug positioned within a tube to be corrugated isprovided for bulging the walls of the tube outwardly into the grooves.The apparatus also includes means for closing a bulge thus formed in thetube to form therefrom a corrugation. These means advanta geouslycomprise a pair of closure plates mounted one over each die plate anddefining between them a tubereceiving opening of the same size and shapeas the die opening, and axially aligned therewith. The closure platesare mounted so as to be movable toward and away from the die plates,thereby to permit closing into a corrugation a bulge in a. tube grippedbetween the closure plates and the die plates.

To facilitate operation of the apparatus, a pair of locating plates maybe mounted one over each closure plate and spaced therefrom a distancecorresponding to the thickness of a corrugation. The locating platesengage between the corrugations of the previously corrugated portion ofthe tube being corrugated and assist in locating the corrugation-closureplates in the proper position preliminary to closing a bulge into acorrugation.

Spacers between the closure plates and the die plates advantageously areprovided to limit movement of the closure plate toward the die plate toprevent excessive flattening of a corrugation as it is being formed bysuch movement from a previously formed bulge.

An advantageous embodiment of the invention is described in greaterdetail below with reference to the manufacture of flexible seamlesscorrugated metal tub.- ing of rectangular cross section. It isunderstood, however, that the following description is also applicableto tubing of other polygonal cross sections. The description ispresented in connection with the accompanying drawings, in which:

. Fig. 1 is a longitudinal section through apparatus for producingcorrugated rectangular seamless tubing in accordance with the invention;

Fig. 2 is another longitudinal section through the apparatus, taken atright angles to the section shown in Fig. 1;

Fig. 3 is a view of the tube-corrugating apparatus taken along the line3-3 of Fig. 1;

Fig. 4 shows a column for transmitting force from a press ram to thecorrugation-closure assembly;

Fig. 5 is a cross section taken substantially alongthe line 5e5 of Fig.4;

Fig. 6 is a plan of a deformable plug used in initially bulging the wallof a rectangular tube to be corrugated in the apparatus shown in Figs. 1to 3;

Fig. 7 is an elevation of the plug shown in Fig. 6;

Fig. 8 is an end view of the plug shown in Figs. 6 and 7;

Figs. 9 to 12 are sections on an enlarged scale through the die platesand closure plates in the region of the die opening, showing successivestages in the tube corrugation operations;

Fig. 13 is a horizontal section taken substantially along the line 13-13of Fig. 10;

Fig. 14 is a cross section taken substantially along the line 1414 ofFig. 11;

Fig. 15 is a fragmentary plan of one half of'the closure plate assembly;

Fig. 16 is a plan of a rectangular tube as it appears while beingcorrugated in accordance with the invention,

showing the bulges formed preliminary to forming the corrugations;

Fig. 17 is an elevation of rectangular corrugated seamless tubingaccording to the invention;

Fig. 18 is a cross section through the tubing shown in Fig. 17;

Fig. 19 is an elevation of a flexible wave guide made from rectangularflexible corrugated tubing according to the invention.

Fig. 20 is an end view of the wave guide shown in Fig. 19;

Fig. 21 is a section through a modified form of apparatus for producingcorrugated tubing in accordance with the invention; and

Fig. 22 is an elevation of tubing as it appears in the course ofmanufacture by means of apparatus as shown in Fig. 21.

Referring to Figs. 1 to 3, the tubing-corrugating apparatus comprises apair of separable die plates 25 formed with horizontal flanges 26. Thedie plates are supported on a base plate 27 which in turn is supportedon a press platform or other supporting structure 28. Guides 29 formedintegrally with the base plate 27, or fastened thereto, define a channelin which the die plates 25 may move toward or away from each other.Retaining plates 30 bolted to the guides 29 and overlying the topsurface of the die plate flanges 26 confine the die plates to movementtoward and away from each other in this channel.

Holes 31 are drilled in the die plate flanges 26 to receive compressionsprings 32 which urge the die plates apart. Cam locks 33 may be rotatedby handles 34 to move the die plates together against the force of thecompression springs 32 and to lock the die plates in this closedposition.

Each of the die plates is formed with a channel in that edge which bearsagainst the adjacent edge of the other die plate, and when the two dieplates are brought together by the cam locks 33, these channels are inregistry so as to form the rectangular die opening in which arectangular tube 35 to be corrugated is received. The tube 35, ofcourse, fits quite snugly in the die opening, which is of the particularsize and shape required to insure such fit of the tube to be corrugated.Oversize openings in the base plate 27 and in the press platform 28,directly beneath the die opening between the die plates 25, permit thetube 35 to enter the die opening from beneath the press platform.

The die plate walls defining this tube opening are formed with upper andlower peripheral grooves 36 and 37 into which the walls of the tube 35may be bulged upon application of an expansive force within the tube.

The means for applying the expansive bulging force within the tube 35comprises a lower mandrel 3S bearing at its lower end against a platform39 and terminating at its upper end just below the lower edge of thelower peripheral groove 37. This mandrel extends up through the tube 35to be corrugated, and its cross-sectional dimensions are such that itfits fairly snugly within the tube 35. The lower end 40 of this lowermandrel may be of reduced size to fit within a socket 41 in the platform39, to prevent it from being accidentally displaced from properalignment with the die opening between the die plates 25.

An upper mandrel 42, similar in cross-sectional size and shape to thelower mandrel 38, extends into the upper portion of the tube 35. Theupper end 43 of this mandrel is of reduced size to fit within a socket44 formed in a press ram 45, and to provide a shoulder 46 against whichthe press ram may bear to apply force to the mandrel 42. As with thesimilar arrangement of the lower mandrel, the reduced end 43 of theupper mandrel 42 is held in the press ram socket 44 to prevent the uppermandrel from being accidentally dislodged from proper alignment with thedie opening.

Located within the tube 35 between the mandrels 38 and 42 are a pair ofdeformable but substantially incompressible plugs 47 and 48. When thepress ram 45 is forced downwardly and exerts pressure against theshoulder 46 of the upper mandrel 42, these plugs are squeezed betweenthe two mandrels and deform, transmitting a bulging force to the wallsof the tube 35 and causing it to be bulged outwardly into the grooves 36and 37.

The deformable plugs 47 and 48 advantageously are of rubber and areconfigured as shown in Figs. 6 to 8. As shown, each plug comprises asubstantially rectangular body or base portion 49 surmounted by apyramidal roof portion 50. The base portion of the plug is of a lengthand breadth such that it fits fairly snugly within the tube 35 to becorrugated, and is of a height approximately equal to the height of thebulge formed by its deformation. The pyramidal roof portion 50 of theplug provides the excess of rubber necessary to expand the tube into thegrooves 36 and 37 in the die plates, and advantageously this pyramidalroof section is truncated as shown in the drawings, so that the base ofthe upper plug 47 will have a good bearing surface against the roof ofthe lower plug 48 when the two plugs are positioned within the tubeduring corrugating operations.

It is generally preferable to apply somewhat greater bulging force tothe corners of the tube being corrugated than to its sides, and for thispurpose the sides 51 of the plug base portion 49 advantageously areslightly concave, as indicated especially in Fig. 6. However, especiallywhen the tube to be corrugated is of fairly heavy wall-thickness, it isnot essential that the sides of the plug be concave.

The provision of two peripheral grooves 36 and 37, and two correspondingplugs 47 and 48, leads to final formation of the bulge in two steps andis advantageous to insure formation of a full-depth bulge which isuniform about the periphery of the tube 35. After initial bulging of thetube into the lower groove 37, the tube is raised a distance such thatthe bulge formed in this groove is brought into alignment with the uppergroove 36, and in this position the bulging operation is repeated. Thebulge preliminarily formed in the lower groove 37 thus is completelyformed in the upper groove 36 in the next subsequent bulging operation.If desired, the lower groove 37 may be slightly shallower than the uppergroove 36, but this is not essential.

An important advantage of the use of two deformable plugs is that theupper plug and groove prevent deformation of the bulge positioned inthat groove when the next bulge is formed in the lower groove by thedeformation of the lower plug. When a bulge is formed in the lowergroove, metal is drawn up from below the lower groove, and would also bedrawn down from the bulge in the upper groove except for the fact thatthe upper plug holds the bulge firmly in the upper groove. If anysubstantial amount of metal is drawn down from the bulge in the uppergroove, the resulting deformation of the upper bulge, especially at thecorners, leads to creasing and cracking of the metal when the bulge issubsequently closed into a corrugation. This effect is particularlypronounced with thin gauge metal. Thus bulging in two steps, even whenthe two grooves are of the same depth, insures that the tube will beadequately and uniformly bulged completely about its periphery andparticularly at the corners, so that subsequent closure of a bulge intoa corrugation will not cause creasing or rupturing of the corrugation atthe corners, where the metal is most severely worked and subjected tomaximum stresses, and so that the corrugations will be of uniform sizeand inside diameter.

After bulging the tube 35 outwardly and peripherally, the next step isto close the bulge thus formed into a corrugation. For this purpose theapparatus is provided with a corrugation-closure plate assembly 52. Thisassembly comprises a pair of closure plates 53 each mounted above one ofthe die plates 25, and each recessed at that edge which meets with thecorresponding edge of the other closure plate, so as to form between theplates a tube-receiving opening of substantially the same size and shapeas the die opening between the die plates, and axially alignedtherewith. A pair of locating plates 54, which are shown in the drawingsas being of the same size and configuration as the closure plates 53,are fastened one to each closure plate with a spacer 55 between them.These spacers separate the locating plates from the closure plates by adistance'corresponding to the thickness of a finished corrugation. Asecond pair of spacers 56, also of a thickness equal to the thickness ofa corrugation and arranged below the closure plates 53, and a pair ofcover plates 57, complete the closure plate assemblies. Each assembly isheld together by screws 58 passing through the several plates andspacers and threaded into the bottom spacers 56.

Press fitted into each closure plate assembly is a pair of dowel-pins 59which enter dowel-pin holes 60 drilled or bored in the die plates. Thedowel-pin locate the closure plate assemblies on the die plates andprevent lateral movement of these parts relative to each other, butpermit movement of the closure plate assemblies toward and away from thecorresponding die plates.

After a bulge has been formed in the wall of the tube 35 beingcorrugated, it is raised (as stated above) by an amount such that thebulge formed in the lower peripheral groove 37 is aligned with the upperperipheral groove 36. When so raised, the bulge that had been finallyformed in the upper peripheral groove 36 now is located with the base ofits lowerside bearing against the die plates at the edge of the dieopening. In this position, the closure plate assemblies must be raisedfrom the die plate sufficiently to permit the closure plates 53 toembrace the bulged tube and to bear against the upperside of the bulgeat its base. Then, when a force is applied to the closure plate assemblyto force it down against the die plate, the bulge gripped between theclosure plates and the die plates is narrowed and deepened into acorrugation. The spacers 56 at the bottom of the closure plateassemblies limit movement of these assemblies toward the die plates, sothat when the bulge'is narrowed into a corrugation it is not excessivelyflattened. The locating plates 54, which engage the corrugated tube overthe corrugation just above that being formed, facilitate locating theclosure plate assemblies at the proper distance above the die plateseach time the tube is raised to perform the operations resulting information of a further corrugation.

In order to apply pressure to the closure plate assembly, a column 61(Figs. 4 and 5) is provided. This column advantageously is made offairly heavy-walled tubing having .a longitudinal segment cut from it,so that it is essentiallyin the form of a channel. The ends of thechannel column may be reinforced by flanges 62. The length of the columnis somewhat greater than the effective length of the upper mandrel 42from the top surface of the closure plate assembly to the shoulder 46.The column 61 therefore may be placed in position substantiallysurrounding the upper mandrel 42, with its lower end bearing against thetop surfaces of the closure plate assemblies and with its upper endsomewhat above the mandrel shoulder 46' With the column thus inposition, downward movement of the ram 45 brings the ram into contactwith the upper end of the column and results in the force of the rambeing transmitted through the column to the closure plate, without anyforce being eXertedon the mandrel 42. Thus, when a bulge in the tubewall is gripped between the closure plates 53 and the die plates 25, andwhen the column 61 is in position substantially surrounding the mandreland bearing against the closure plate assembly, the same ram 45' usedfor applying force to the mandrel 42 to form the bulge now may serve toapply force to the closure plate assemblies for the purpose :ofnarrowing and deepening the bulge into a corrugation. The channel shapeof the column facilitates placing it in position about the mandrel andremoving it from such position, as required in the sequence, ofoperations performed in first bulging the tubing and then closing thebulge to form a corrugation.

The sequence of operations involved in using the abovedescribedapparatus to corrugate rectangular seamless metal tubing is illustratedin Figs. 9 to 12, which incidentally show the abutting portions of thedie plate and closure plate assemblies on an enlarged scale. Fig. 9shows the tube 35 being corrugated in a position that may be termed thestarting position in the sequence of operations involved in forming eachcorrugation. As shown in this figure, the tube has just been raised sothat the initially formed bulge 63 is in position to be finally formedin the upper peripheral groove in the die plates 25, while that portion64 of the tubing which is in position adjacent the lower groove 37 hasnot yet been bulged. The bulge 65 which was finally formed in thepreceding sequence of operations is gripped between the upper surface ofthe die plates 25 and the closure plates 53. The closure plates havebeen located in the proper position with the aid of the locating plates54-, which engage the tubing just above the last-formed corrugation 66.Above the locating plate 54 is the corrugated portion 67 of the tubingwhich was formed during preceding corrugationforming operations. Thelower mandrel 38 is in position in the tube 35, with the undeformedplugs 47 and 48 immediately over it and approximately opposite theperiph eral grooves in the die plates. The upper mandrel 42 extendsthrough the corrugated upper portion of the tubing into position forapplying force to the plugs.

In the next step, as shown in Fig. 10, force is applied to the uppermandrel 42, thereby deforming the plugs 47 and 48. The deformed lowerplug 48 bulges the wall of the tube 35 out into the lower peripheralgroove, initially forming a new lower bulge 68. At the same time thebulge 63 is finally formed, by deformation of the upper plug 47, into afull-depth bulge which is substantially uniform about the periphery ofthe tube 35. During this operation the closure plate assemblies 52remain in the same position as before In the first step of the bulgingoperation, illustrated in Fig. 11, the force on the upper mandrel 42 isreleased and the column 61 is placed in position substantiallysurrounding this mandrel, with its lower end bearing against the topsurface of the closure plate assemblies 52. Force then is applied to thecolumn 61, forcing the closure plate assemblies down toward the dieplates 25. The applied force results in squeezing the bulge (65 in Figs.9 and 10) which was gripped between the closure plates 53 and the topsurfaces of the die plates into the narrowed and deepened form of a newcorrugation 69 (Fig. 11). The spacers 56 at the bottom of the die plateassemblies prevent fiattening the corrugation 69 beyond the desiredlimit.

The final step (illustrated in Fig. 12) is to raise the tube 35 intoposition for repeating the above-described sequence of operations. To doso, the cam lock holding the right-hand die plate 25 in position isreleased, and this die plate is thereupon pushed away from the lefthanddie plate by the action of the compression springs 32,. This results indisengaging the right-hand die plate and the right-hand closure plateassemblies 52 from the corrugated and bulged tubing. It is now possibleto tilt the tube 35 and the mandrels 38 and 42 sufficiently to the rightto disengage the bulged tubing from the grooves 36 and 37 in theleft-hand die plate, and the corrugations from the left-hand closureplate 53 and locating plate 54. The tube then may be moved up manuallyalong the mandrels sufficiently to bring the last-formed bulge 68opposite the upper groove 36. The tube 35 then is tilted back to theleft so that the lowest bulge 68 enters the upper groove 36 in theleft-hand die plate; and at the same time the left-hand closure plateassembly is lifted up from the die plate and manipulatedso that theclosure plate 53 engages with the tubing over the now finally formedbulge 63 and just below the last-formed corrugation 69, and the locatingplate 54 engages the tubing just above this corrugation. With the tubethus repositioned in the left-hand die plate and left-hand closure plateassemblies, the right-hand die plate and closure plate assemblies maynow be brought back by operation of the right-hand cam lock, into closedposition with the corresponding left-hand members. At the completion ofthis operation, the apparatus is again in the position illustrated inFig. 9, and the above-described sequence of operations may be repeatedto form another corrugation.

In the hands of a practiced operator, manipulation of the apparatus asabove-described may be carried out rapidly and without damage to thetubing, even though it may be very thin-walled.

It is not essential to tilt the tubing, as described above in connectionwith Fig. 12, in advancing it upwardly. If desired, both rightandleft-hand cam locks 33 may be released, and the tubing may be moved upwhile still perfectly straight. In general, however, tilting the tube asdescribed permits of more rapid and convenient operation of theapparatus.

The apparatus has been described with particular reference tohand-operation, but it is understood that it may be operatedautomatically. It may be fully automatic in operation, so that openingand closing of the die plates, upward advance of the tubing, andoperation of the ram all are eflected automatically; or if desired theapparatus may be designed so that some of these operations are automaticwhile others are hand-performed or hand controlled.

Tubing as it appears in the course of being corrugated is shown in Fig.16. Immediately above the uncorrugated seamless tubing blank 35 are thebulged sections 63 and 65, and above this is the finished corrugatedsection 67.

Figs. 17 and 18 illustrate a completed length of corrugated tubing 70.In this tubing, all bulges have been narrowed and deepened intocorrugations 71. The corrugations are relatively deep and narrow, andare spaced apart a distance approximating their depth. As best shown inFig. 18, the tubing is substantially rectangular in cross section. Atthe corners of the tubing, however, the outer surfaces 72 of thecorrugations are formed with a substantial radius of curvature. Thedepth of the corrugations is substantially, if not quite, as great atthe corners as in the middle of the side or edge wall of the tube. Inconsequence of these relatively deep, narrow and closely spacedcorrugations, the tubing is extremely flexible and may be bent through ashort radius, either sidewise or edgewise.

The new tubing is admirably suited for use in making flexible waveguides, of which one form is shown in Figs. 19 and 20. The wave guideshown comprises a length of corrugated seamless metal tubing 73 ofrectangular cross section. The dimensions of the tubing are, of course,preselected according to the wave length of the radiation to betransmitted through the guide. End fittings 74 are brazed or otherwisesecured to the ends of the length of tubing 73. The end fittings areformed with a substantially central opening 75 accurately matched to theminimum inside diameter of the tubing, and is provided with holes 76 formounting purposes.

Flexible wave guides of this character are excellently suited forconnecting rigid wave guides to each other, or to other equipment, atpoints where some flexure is necessary or desirable. Rectangular tubingordinarily is necessary for efficient wave guides, and flexiblecorrugated seamless rectangular metal tubing may be made in acaccordancewith the invention with proper spacing of the corrugations, and with thenecessary uniformity in size and shape of corrugations, to insureminimum power losses due to reflection or other causes when the tubingis employed in the manufacture of flexible wave guides.

While tubing produced in acordance with the invention is extremelyflexible to bending forces applied parallel to a side or edge, it isresistant to torsion forces. Also, when a bending force is applied tothe tubing, the closely spaced corrugations each accommodatesubstantially equal increments of the total bending force, so that evenwhen the tubing is bent, uniformity in spacing of the corrugations ispreserved. These characteristics make the new tubing very useful forwave guide purposes, and for other uses as well.

The invention has been particularly described above in connection withthe manufacture of flexible corrugated seamless metal tubing inapparatus comprising die plates formed with two peripheral grooves inthe walls of the die opening, but in some instances a single peripheralgroove is sufiicient. Particular mention also has been made above of aclosure plate assembly including a locating plate, but if desired thisplate may be omitted. Apparatus embodying these modifications is shownin Fig. 21. In this modification, separable die plates 77 form betweenthem a die opening in which a rectangular metal tube 78 is positioned;and but a single peripheral groove 79, into which the tube 78 is to bebulged, is formed in the die plate walls defining the die opening.Otherwise the die plates 77 may be made and mounted similarly to the dieplates 25 described above.

As shown in Fig. 21, only a single deformable plug 80 is positionedbetween the ends of a lower mandrel 81 and an upper mandrel 82. Closureplate assemblies 83 each having only a closure plate 84, a cover plate85, and a spacer 86, are provided to narrow and deepen the bulges formedin the tubing stock into corrugations.

Fig. 21 shows the modified apparatus with the tubing in the positioncorresponding to that shown in Fig. 9, described above. The sequence ofoperations involved in using this apparatus, including (1) applyingforce to the mandrel 82 to bulge the tube outwardly into the groove 7 8,(2) subsequently applying pressure to the closure plate assembly 83 (theclosure plate 84 of which engages the upper side of a previously formedbulge 87) to deepen and narrow the bulge into a corrugation, and (3)thereafter raising the tubing 78 into position for repeating thissequence of operations, may be as described above with reference toFigs. 9 to 12.

Fig. 22 is a side view of the rectangular corrugated metal tubing as itappears during manufacture with the use of apparatus as shown in Fig.21. Above the lower uncorrugated portion of the rectangular tube stock78 is the single bulge 87, and above this is the corrugated portion 88previously formed in the manufacturing process.

While the apparatus and method of the invention have been describedspecifically with reference to the manufacture of rectangular corrugatedseamless metal tubing, they are equally applicable to the manufacture ofcorrugated seamless metal tubing of other polygonal cross sections, suchas corrugated seamless metal tubing of pentagonal, hexagonal oroctagonal cross section. The only major change required in the apparatusdescribed above to make corrugated seamless metal tubing of these otherpolygonal cross sections is to make the die opening of the shape andsize desired, and to make the upper and lower mandrels and thedeformable plugs of the corresponding cross-sectional shape and size.The method of making corrugated seamless metal tubing of these othercross-sectional shapes is essentially the same as herein described formaking the rectangular tubing.

As with the rectangular tubing, flexible corrugated seamless metaltubing of these other polygonal cross sections is characterized byhaving a plurality of deep and narrow annular corrugations, spaced aparta distance approximating their depth, and with the outer surfaces of thecorrugations being formed with a substantial radius of curvature at thecorners of the tubing.

It is evident that other modifications than those specifically describedherein may be made within the scope of the invention.

I claim:

1. Apparatus for manufacturing seamless corrugated flexible metal tubingof rectangular or other polygonal cross section comprising a pair of dieplates each formed with a tube-receiving channel in an edge thereof, thewalls defining said channel being peripherally grooved, means forbringing said die plates into closed engagement with the channels inregistry so as to form a polygonal die opening for receiving arectangular or other polygonal seamless tube and with the peripheralgrooves therein also in registry, a lower mandrel for insertion into arectangular or other polygonal tube positioned in said die opening andhaving its upper end adjacent the lowermost internal groove, adeformable but substantially incompressible plug for insertion into saidtube directly above said lower mandrel, an upper mandrel for insertioninto said tube with its upper end overlying said plug, means for movingone mandrel toward the other to deform the plug and expand the tube intothe peripheral groove, thereby forming a fulldepth outward bulge ofsubstantially uniform wall thickness completely about the periphery ofthe rectangular tube, corrugation-forming means cooperating with saiddie plates for engaging the bulged tube on both sides of the bulgeadjacent the base thereof, and means for applying pressure to saidcorrugation-forming means in such manner as to narrow and deepen thebulge into a corrugation of substantially uniform wall thickness.

2. Apparatus for manufacturing seamless corrugated flexible metal tubingof rectangular or other polygonal cross section comprising a pair of dieplates each formed with a tube-receiving channel in an edge thereof, thewalls defining said channels being peripherally grooved, means forbringing said die plates into closed engagement with the channels inregistry so as to form a polygonal die opening for receiving arectangular or other polygonal seamless tube and with the peripheralgrooves also in registry, a deformable but substantially incompressibleplug for insertion into a rectangular or other polygonal tube positionedwithin said die opening, upper and lower mandrels for insertion intosaid tube above and below said plug and confining the plug to the regionadjacent the peripheral grooves in the die plate, means acting on atleast one mandrel for squeezing the plug between the mandrels andexpanding the walls of the tube into the peripheral grooves, therebyforming outward bulges completely about the periphery of the tube, acorrugation closure plate mounted above each die plate and each formedwith a tube-receiving aperture, means for bringing said closure platestogether with the apertures therein in registry, said closure platesbeing adapted to embrace a bulged tube with the edges of the aperturestherein engaging one side of the bulge adjacent the base thereof whilethe other side of the bulge is engaged at the base thereof by the dieplate at the edge of the die opening, and means for pressing the closureplates against the die plates to pinch the bulge in the tubetherebetween, thereby narrowing and deepening the bulge into acorrugation.

3. In apparatus of the character described, a pair of die plates eachformed with a tube-receiving channel in an edge thereof, the wallsdefining said channel in each die plate being formed with a pair ofspaced peripheral grooves, means for bringing and locking the die platestogether with the channels therein in registry to form a polygonal dieopening and with the grooves also in registry to form a pair of spacedperipheral grooves into which the walls of a polygonal metal tube can bebulged, means for bulging the walls of a tube positioned in said dieopening outwardly into said grooves, and separable corrugating means forclosing a bulge thus formed in said tube to form therefrom acorrugation, said corrugating means being constructed with an opening toreceive the work and being disposed adjacent the die opening formed insaid pair of die plates and being adapted to move toward and away fromsaid die plates, said corrugating means also being constructed to engagewith the side of a bulge 10 formed in the tube, and in movement of thecorrugating means toward the die plates to compress a bulge between itand the die plates, when the work has been advanced out of the dieopening to position a bulge between the die plates and the corrugatingmeans.

4. In apparatus of the character described, a pair of die plates eachformed with a substantially rectangular tube-receiving channel in anedge thereof, the walls defining said channel in each die plate beingformed with. a pair of spaced peripheral grooves, spring means urgingthe die plates apart, means for bringing and locking the die platestogether against the force of the springs with the channels therein inregistry to form a die opening and with the grooves also in registry toform a pair of spaced peripheral grooves into which the walls of arectangular metal tube can be bulged, means for bulging the walls of atube positioned in said die opening outwardly into said grooves, andseparable corrugating means for closing a bulge thus formed in said tubeto form therefrom a corrugation, said corrugating means beingconstructed with an opening to receive the work and being disposedadjacent the die opening formed in said pair of die plates and beingadapted to move toward and away from said die plates, said corrugatingmeans also being constructed to engage with the side of a bulge formedin the tube, and in movement of the corrugating means toward the dieplates to compress a bulge between it and the die plates, when the workhas been advanced out of the die opening to position a bulge between thedie plates and the corrugating means.

5. In apparatus of the character described, a pair of separable dieplates defining between them a polygonal die opening having on its innersurface a pair of spaced polygonal grooves into which the walls of apolygonal metal tube can be bulged, and a pair of separable corrugationclosure plates mounted one over each die plate and defining between thema tube-receiving opening of substantially the same size and shape as thedie opening and axially aligned therewith, said closure plates beingmovable toward and away from the die plates so as to permit closing abulge in a tube gripped between the closure plates and the die platesinto a corrugation.

6. In apparatus of the character described, a pair of separable dieplates defining between them a polygonal die opening, a pair of closureplates mounted one over each die plate and defining between them atube-receiving opening of substantially the same size and shape as thedie opening and axially aligned therewith, and a pair of locating platesmounted one over each closure plate and spaced therefrom a distancecorresponding to the thickness of a corrugation in a tube beingcorrugated, the assembly of closure plates and locating plates beingmovable toward and away from the die plates so as to permit closing intoa corrugation a bulge in a tube gripped between the closure plates andthe die plates.

7. In apparatus of the character described, a pair of separable dieplates defining between them a polygonal die opening, a pair of closureplates mounted one over each die plate and defining between them atube-receiving opening of substantially the same size and shape as thedie opening and axially aligned therewith, a pair of locating platesmounted one over each closure plate and spaced therefrom a distancecorresponding to the thickness of a corrugation in a tube beingcorrugated, the assembly of closure plates and locating plates beingmovable toward and away from the die plates so as to permit closing intoa corrugation a bulge in a tube gripped between the closure plates andthe die plates, and spacers between the closure plates and the dieplates to limit movement of the closure plates toward the die plates toprevent excessive flattening of a corrugation as it is being formed bysuch movement.

8. In apparatus of the character described, a plug for forming anoutward peripheral bulge on a polygonal tube to be corrugated comprisinga polygonal body portion of deformable substantially incompressiblematerial, surmounted by a pyramidal roof portion of such material.

9. In apparatus of the character described, a plug for forming anoutward peripheral bulge on a polygonal tube to be corrugated, said plugbeing composed of deformable substantially incompressible material andcomprising a polygonal body portion integrally united with a roofportion in the form of a truncated pyramid, at least some sides of saidbody portion being slightly concave.

10. In apparatus of the character described comprising a mandrel adaptedto be moved axially to deform a plug and so produce an outward bulge ona tube to be corrugated, a closure plate assembly adapted to be moved toclose such bulge into a corrugation, and a ram for applying force bothto the mandrel and to the closure plate assembly, means for transmittingforce from the ram to the closure plate without actuating the mandrelcomprising a column substantially channel-shaped in cross section, theopen side of the channel-column being of sulficient width to permit thecolumn to be placed in position substantially surrounding the mandreland bearing against the upper surface of the closure plate assembly, andthe effective length of said column being greater than the effectivelength of the mandrel between the ram and the upper surface of theclosure plate assembly.

11. The method of making seamless corrugated flexible metal tubing ofpolygonal cross section which comprises forming an outward peripheralbulge completely around a 12 polygonal seamless metal tube by applying asomewhat greater bulging pressure at the corners of the tube than at thesides thereof while confining within a polygonal die the portions of thetube adjacent the portion thereof being bulged, and subsequentlynarrowing and deepening the bulge into a corrugation.

12. The method of making seamless corrugated flexible metal tubing ofpolygonal cross section which comprises bulging a polygonal seamlessmetal tube outwardly and peripherally by applying pressure to adeformable plug within the tube and transmitting through said plugsomewhat greater bulging pressure at the corners of the tube than at thesides thereof while confining within a polygonal die the portions of thetube adjacent the portion thereof being bulged, and subsequentlynarrowing and deepening the bulge into a corrugation.

References Cited in the file of this patent UNITED STATES PATENTS1,605,194 Kopf Nov. 2, 1926 1,754,922 Weldon Apr. 15, 1930 1,879,663Dreyer Sept. 27, 1932 2,306,018 Frentress Dec. 22, 1942 FOREIGN PATENTS23,828 Great Britain of 1896

